added portproxy post meterpreter module
OptEnum option changed
Juan changes applied
Beautify metadata
Favor unless over if not
Use datastore options to avoid complex logic around args
Avoid redefine builtin datastore options
Use OptPort
Reduce code complexity on check_ipv6
Omit parentheses for method call with no args
Delete vague exception handling only done on one place
Move the check_ipv6 call to the run metod
Provide more information about installing IPv6
Land #2283, @bmerinofe's post module for PortProxy Port Forwarding
Add metsrv.dll updates for proxy support

See #1033, #2014, and meterpreter/#12